YPO4 and Mg2P2O7 mixed ceramic semiconductor samples were .........prepared and investigated to be used as humidity sensors. The samples were characterized using XRD. Surface area, SEM, and electrical conductivity under the effect of humidity at room temperature were measured and discussed. X-ray patterns showed the formation of YPO4 in tetragonal phase and Mg2P2O7 in monoclinic form. Adding Mg2P2O7 improves the surface area of YPO4 which affected the electric conductivity. The humidity sensing of the pure and mixture samples was studied by dependences of the electrical conductivity on the mixture content and the sensitivity was also calculated. The results indicated that the electrical conductivity increased as relative humidity increased up to 76% due to the protonic conductivity which specified the action of water content on the phosphate molecules. After 76% relative humidity (RH), the value the electrical conductivity and sensitivity started to decrease due to the blocking of the phosphates molecules under high humidity value.